It is well-known that in sufficiently moist or damp conditions almost any building material can become mouldy, i.e. growth of fungi occurs on the surface of the materials, frequently to an extent where the fungal growth becomes visually recognizable optionally in the form of disfigurements on the building material surface.
Development of indoor fungal contamination is influenced by moisture, nutrients, pH, temperature and light, of which moisture is the most important. Fungal growth is predominantly controlled by the water content of the surface of a material and the relative humidity (RH) of the air which has an indirect influence through drying or moistening the material. In case of hygric equilibrium between air and the material, fungal growth is likely to occur when the RH exceeds 76-96% depending on fungal species, temperature, time, composition and hygroscopicity of a material. Fungal species can grow within a rather wide temperature range such as 0 to 40.degree. C., the specific temperature range depending on the species.
Such a high moisture content in buildings typically results from condensation of ambient moisture on cold surfaces, water leakages from plumbing constructions or through leaky roofs or cellar walls, or ventilation rates which are inadequate to remove the moisture in the building. Additionally, high amounts of moisture may be generated directly by occupants or by their activities such as bathing, cleaning or cooking. Thus, high indoor moisture contents are typically found in buildings with a high density of occupants such as in schools, day-care centres and office buildings.
Mouldy buildings are commonly found in areas with temperate or cold climates, since under such climatic conditions, the outdoor/indoor temperature difference is high, in particular during winter. However, such temperature differences will also occur in tropic and subtropic regions during summer where buildings are cooled.
Most building materials are porous. When condensation of water near cold surfaces occurs, the condensed water will be absorbed by the porous surface material. Under these circumstances, the moisture content of the surface material may increase significantly up to highly wet levels not far from saturation. Surface condensation of water vapour is thus considered to be one of the major causes of fungal disfigurements of buildings.
In the present context, the term "buildings" includes buildings where farm animals are kept, such as stables, cowsheds, studs, barns and premises for keeping pigs. The climatic conditions including the moisture content in such animal premises are frequently such that good conditions for fungal growth are provided which may result in fungal contamination of the surface materials in these premises resulting in a poor indoor quality for human individuals working in such buildings. Accordingly, fungal contamination of animal premises can become a serious occupational health risk for farm labourers. It is contemplated that the present method is very useful for controlling the fungal contamination of the above premises with the objective of improving the indoor quality therein.
Under the above moisture conditions, fungal contamination of indoor building materials may build up to levels which have adverse health implications for those individuals occupying the building. Systemic or local symptoms ascribable to the load of fungal contamination will primarily occur as a result of fungal material or metabolites being released from the contaminated surfaces into the indoor air. During the last decade it has been recognized that a high fungal contamination of indoor air may cause serious health problems. Thus, certain fungal species may influence the immune system negatively or cause serious infections in subjects having an immune deficiency e.g. caused by HIV or by an immunosuppressive treatment such as in cancer patients subjected to chemotherapy or radiotherapy. Additionally, fungi in indoor air may cause allergy symptoms or they may have a direct toxic effect due to the production of toxic metabolites i.e. mycotoxins. One particular pathogenic, toxin-producing fungal species which is often found in moist buildings is Stachybotrys atra.
Frequently, however, fungal contamination of indoor air gives rise to a syndrome of more general symptoms of a non-specific nature. This syndrome is referred to by the WHO as Sick Building Syndrome.
The presently available measures to eliminate or control fungal contamination problems in buildings include:
(i) Remediation measures whereby heavily contaminated construction elements are removed, optionally followed by suitable measures to reduce the moisture content to levels which prevent renewed build-up of contamination including improved ventilation and removal of sources of moisture. Obviously, such a measure is very costly. PA1 (ii) Removal of visible fungal growth e.g. by vacuum cleaning followed by applying fungicidal chemicals substances onto the contaminated building material surfaces. Such a method is disclosed in EP-A-355 765 where a quaternary ammonium compound is used for treating interior surfaces and ventilation systems. Other fungicidal substances presently used for controlling fungal contamination of building structures include disodium-octaborate-tetrahydrate, benzalconium chloride and pyrocatechin. The disadvantages of using chemical control of fungal contamination are clearly that the application hereof may have toxic side effects on occupants or give rise to unacceptable off-odours and that those applying the substances need to carry protective garments and devices. PA1 (iii) It is known to destroy attacks in buildings by the dry rot fungus, Merulius lacrymans by treating wood constructions with hot air at about 90.degree. C. which temperature has to be maintained for hours or even days to obtain a wood core temperature of 50-60.degree. C. However, such an extreme thermal treatment cannot be used generally to directly reduce fungal contamination on surfaces of building structures. Such a treatment is costly, and more importantly, such a long-term thermal treatment of building materials will inevitably cause damages to e.g. electrical installations, or it will cause deformations e.g. of plastic based materials and deteriorate glue based joinings. PA1 (iv) It has also been attempted to control fungal growth on building structures by conditioning the air by introducing dry air at a temperature of about 50-60.degree. C. to reduce the indoor moisture content to levels where fungal growth is inhibited. Such a measure is disclosed in DE-A-3 338 848 and EP-A-143 324. However, such a measure is not effective with regard to inactivating the fungal spores, and dried surfaces are more prone to become recontaminated. Furthermore, this measure has to be repeated continuously to be effective and thus, it is costly.
In a recent Danish report on mould fungi in public buildings ("Skimmelsvampe i offentlige bygninger" published by Forlaget Kommuneinformation, 1995) it was concluded that none of the presently available measures for controlling fungal contamination in buildings are acceptable or suitable for the reasons mentioned above, and the report states that the only remaining possibility to control fungal growth in buildings is the replacement of contaminated materials with clean materials. It is currently anticipated that the total costs for such remediation initiatives which need to be taken in public buildings in Denmark may amount to several billion US dollars.
A strong need therefore exists to provide an alternative method of removing and controlling fungal contamination of building structures as a means of improving the indoor air quality in the buildings, which is effective, non-toxic and cost-effective.
It is known to use steam generating apparatuses for conventional cleaning purposes in indoor environments of a normal hygienic standard including residential and industrial buildings such as e.g. food production facilities, which are not suffering from fungal contamination to the extent as is described herein, i.e. not to an extent where occupants suffer from symptoms generally associated with fungal contamination. However, it has not been suggested that the use of water vapour-derived energy provides a useful and effective means of controlling such extensive fungal contamination on building structures.
It has now surprisingly been found that an alternative, cost-effective and safe method of controlling fungal contamination of building structures can be provided which is based on applying a high amount of thermal energy derived from water vapour under pressure onto fungally contaminated building material surfaces for a short period, i.e. seconds or few minutes whereby effective inactivation of fungal mycelia and spores is obtained without damages to the building materials.